Not every single e-mail requires that you track it in @Waiting For; it's only necessary if you *really* care about getting a response or the execution of your work depends on it. Even then, if the list is huge, don't let it drive you crazy. Be thankful that your brain isn't tasked with tracking that huge list!
I have one extra tip to offer Outlook users. You can flag e-mails for follow up and set a time-specific reminder. Look for the red flag button on the toolbar. You don't need to duplicate the reminder in your @Waiting For task list.